Balanced circulating system for refrigeration



R. R. ROSS Dec. 27, 1960 BALANCED CIRCULATING SYSTEM FOR REFRIGERATION 4Sheets-Sheet 1 Filed Aug. 17, 1959 IK\ l@ @WS ANNNK r.. hm@ Summum vBYR. R. Ross 2,966,043

BALANCED CIRCULATING SYSTEM FOR REFRIGERATION Dec. 27, 1960 4Sheets-Sheet 2 Filed Aug. 17, 1959 www Dec. 27, 1960 R. R. Ross2,966,043

BALANCED GIRCULATING SYSTEM FOR REFRIGERATION Filed Aug. 17, 1959 4Sheets-Sheet 3 O/L SEPA/Vl TOR m INVENTOR.

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BY D R. R. ROSS Dec. 27, 1960 BALANCED CIRCULATING SYSTEM FORREFRIGERATION 4 Sheets-Sheet 4 Filed Aug. 17, 1959 f WQ] United StatesPatent O BALAWCED CRCULATING SYSTEM FOR REFRIGERATION Robert R. Ross,Batavia, Ill., assignor to Wayland Phillips, Chicago, Ill.

Filed Aug. 17, 1959, Ser. No. 834,049

9 Claims. (Cl. 62-174) The invention relates to refrigerating systemsand has reference more particularly to large capacity industrial typerefrigerating systems wherein it is necessary to protect the compressorof the system from liquid refrigerants such as would otherwise return inthe suction line to the compressor.

The refrigerant circulating system of the invention is designed forincorporation in the refrigerating system of an industrial plant such asmay operate with multi-stages of compression and with evaporatorsdischarging to the -f high stage compressor suction as well as to thebooster compressor suction. However, the system may also be applied torefrigeration plants using single stage operation with various suctionpressures, provided there is suficient pressure difference between theevaporators to effect the necessary flow requirements.

An object of the invention is to provide improvements in refrigeratingsystems, particularly of the industrial tvpe, whereby complete andconstant circulation of both the liquid and the gaseous refrigerant isaccomplished without adding to the power requirements of the plant.

Another object is to provide improved apparatus for the circulation ofthe liquid refrigerant in a controlled manner and which will be causedto by-pass the compressor of the system so that the evaporators can beoperated continuously and in a flooded condition.

Another object of the invention resides in the provision of arefrigerant circulating system of the type as described, having aconstant pressure dierential for feeding liquid refrigerant to aplurality of evaporators operating at different suction pressures.

A more specific object is to provide a refrigerant circulating systemincorporating the improvements as described and wherein the requiredpressure dierential is produced by using the pressure of the availablegas in the system, thus eliminating the need for additional mechanicalpumps.

Another specific object of the invention is to provide a system ofcirculating a refrigerant and which will use the excess liquidrefrigerant returning from the evaporators at the high suction pressurelevel to feed the evaporators at the low suction pressure level.

A further object is to provide a refrigerant circulating system whichwill use the liquid returning from the high temperature evaporators tosub-cool the liquid fed to these evaporators and which will also use theliquid from the low temperature evaporators to sub-cool the liquid fedto the said low temperature evaporators.

Other obiects and advantages of this invention will be apparent from thefollowing description and the accompanying drawings wherein- Figure l isa diagrammatic view illustrating a refrigerating system havingincorporated therein high and low temperature evaporators with twocompressors, the same comprising the improved combination of theinvention.

Figure 2 is a diagrammatic view of a modified refrigeration systembasically similar to Figure 1 but incorporating two separate liquidreceivers.

Figure 3 is a diagrammatic view illustrating another modifiedrefrigerating system coming within the invention, the same combininghigh and low evaporators with one stage of compression, and

Figure 4 is a diagrammatic view showing a further modified form of theinvention and comprising a single compressor-evaporator system.

Referring to Figure l of the drawings, the numeral 10 indicates a highstage suction line and the numeral 11 the booster suction line forreturning the evaporated refrigerant from the high temperatureevaporators and from the low temperature evaporators respectively. Thedrawings show the refrigerant feeding line to the said evaporators andthe structure for effecting operation of the evaporators according tothe invention will now be described in detail.

From the suction line 10, the returning refrigerant is delivered to themain compressor 12, having the high pressure discharge line 13. Also,for the suction line 11, the returning evaporated refrigerant isdelivered to the booster compressor 14 having the high pressuredischarge line 15. Both compressors are conventional in construction andin operation, being suitably driven so that the low pressure gas fromthe suction lines is increased in pressure and which results in acorresponding increase in temperature. The high pressure discharge line13 delivers into the condenser 16, having an outlet connection 17leading to the receiver i8. The condenser also has associated therewitha pilot receiver 20 and with which is combined the high side oat valve21 and the pilot operated control valve 22, the said pilot valve beinginterposed in the connection 17 leading to the receiver 18.

A considerable pressure difference exists between the condenser 16 andthe receiver 18. Whereas the pressure within the condenser mayapproximate 160 pounds per square inch, which is about the same as thedischarge pressure of the compressor l2, a reduced pressure will existin the receiver and which may range from about 60 to 80 pounds persquare inch. Also, a pressure difference exists between the receiver 18and the high temperature, suction line accumulator 24. The receiver ismaintained at a pressure which is higher than the intermediate pressureof the two stages by means of the pressure differential regulator 25interposed in the connection line 26. The regulator will bleed the flashgas,` which is evolved due to a decrease from the condenser pressure toreceiver pressure, to the accumulator 24 at a controlled rate, thusmaintaining a pressure of about pounds per square inch in theaccumulator, provided the regulator is set for 30 pounds and with areceiver pressure of about pounds. If the accumulator pressure shouldrise to 50 pounds, then the pressure in the receiver will increase toapproximately pounds. It is understood that the pressure difference willbe adjusted to the minimum required level to allow adequate fiow throughthe feed line from the receiver 1S to all of the high temperatureevaporators. The said accumulator receives the evaporated refrigerantgas from the high temperature evaporators through the suction lineconnection 27 and the accumulator will also receive any liquidrefrigerant which may accompany the gas, the same being termed theslop-over and which must bv-nass the compressor. The liquid whichevaporates in the accumulator 24 due to the addition of heat from thesubcooling coil 31, and from the heat gain in desuperheating the gasfrom line 33, is returned by suction line 10 to the compressor 12.

The liquid refrigerant feed line 28 to the high temperature evaporatorsconnects with the receiver at 30 and said line includes a cooling coil31 located within the accumulator 24 and disposed below the level of theliquid refrigerant within the accumulator. From the coil the liquidrefrigerant is fed to the high temperature evaporators. In case theamount of liquid vreturning to the accuni'irl'at'or from the hightemperature'evaporatrs,is irisu'cient quantity to satisfy ytherequirements of the low temperature evaporators, the low levelcontroller 32 will supp-ly the additional quantity as needed from theline' 2'8. The accumulator 24 is also supplied with gaseous refrigerantfrom the discharge line 15 of the booster compressor,v the said highpressure gas being supplied to the open-end conduit 33 which issubmerged in the liquid refrigerant within the accumulator and thus saidgas is cooled and condensedv to the liquid form.

It will be understood that the pressure of the liquid in the intercooler24 will be higher than the suction pressure from the low temperatureevaporators. Thus, the liquid refrigerant from accumulator 24 will besupplied r by line 34 to a cooling coil 35 llocated within the lowtemperature accumulator 36. From said coil, the liquid receiver for thelow temperature evaporator-s, itis necessary to provide a valve such as3S inthe outlet line 34. i

The transfer of the liquid refrigerant from the accu'-Y mulators 24 and36 to the receiver is accomplished by a return system of the typedisclosed and claimed in the Phillips patent, 2,589,859, granted March18, 1952-, and entitled Suction Line Liquid Return Trap. Liquidrefrigerant flows by gravity from accumulator 24 by means of the line40, the said line connecting with the accumulator at a location whichwill maintain the desired liquid level in the accumulator. Line 40connects with the trap 41. When liquid in the trap reaches apre-determined high level7 the differential oat switch 42 will actuatethe three-way valve 43 to connect the top of the trap to the condenser16 by means of the line 44. The high pressure gas from the condenserwill force the liquid within the trap into the receiver 18 through theconnecting lines 45 and 46. When the liquid refrigerant in the trapreaches a pre-determined low limit, the switch 42 will again actu# atethe three-way valve 43 to `close the line 44 and connect the trap withline 47 leading to the accumulator 24. With the accumulator and trapthus equalized in pressure, the liquid refrigerant will again flow byvgravity to the trap. The low temperature accumulator 36 is similarlyconnected by lines 48 and 50 to a trap 51 having a diierential floatswitch 52 andV a Vthree-way valve 53. The structure operates in a mannerexactly similar to that as described for trap 41. Accordingly, theliquid from the accumulators is transferred to receiver 18 by using thehigh pressure gas from the condenser. Also,` the ycirculating system ofFigure l employs the liquid refrigerant returning from the evaporatorsto sub-cool the liquid being fed to these evaporators. In addition aconstant pressure differential is maintained for feeding thev'liquidrefrigerant to the evaporators although the same operate at differentsuction pressures. v

The circulating system of Figure 2 is similar in its basic aspects tothat shown in Figure 1, with the exception that two separate liquidreceivers are employed. Thesuction line 60 and the booster suction line61 connect respectively with the main compressor 62 and the booster orlower suction pressure compressor 63. The' high pressure discharge line64 for the main compressor hasconnection with the discharge line 65 forthe booster compressor and the same in turndeliver to the condenserY 66.The

outlet for the condenser 66 is indicated by numeral 67 and the sameleads to the high temperature receiver 68. The liquid refrigerant flowto the receiver is controlled by the pilot receiver 70 having combinedtherewith the high side tloat valve 71 and the pilot operated valve 72.The receiver 68 has connection at its top through the line 73 with thehigh temperature suction accumulator 74. The pressure differentialregulator 75 maintains the desired pressure dierence between thereceiver and its accumulator. The liquid refrigerant from the receiver68 is supplied by linc 76 to the coil 77 which is submerged by theliquid refrigerant contained within the high temperature suctionaccumulator 74. From the coil 77 the liquid refrigerant feed line 78delivers the refrigerant to the high temperature evaporators which mayconsist of two or more coils 80 connected in parallel and each having anexpansion valve 81. The evaporated gas from the evaporators 8) togetherwith liquid refrigerant entrained by the gas is returned to theaccumulator 74 by the suction line connection 82. Referring again toline 76, it will be noted that a oat valve 83 is interposed in said linetogether with certain hand operated valves for maintaining the desiredliquid level within the accumulator 74 in those instances when the hightemperature evaporators do not provide enough liquid to supply the lowtemperature evaporators.

The second stage of the apparatus of Figure 2 includes a low temperaturereceiver 85 and a `low temperature accumulator 86. The line 87 connectswith the accumulator 74 at its base and said line delivers liquidrefrigerant to the receiver 85 adjacent the upper end of the receiver.The solenoid operated valve 88 is located in the line 87 adjacentreceiver 85. The oat switchr89 controls the solenoid of the valve 88 andthus controls the discharge of liquid refrgerant to the low temperaturereceiver. The float switch 89 therefore mantains a normal liquid levelwithin the receiver. A second connection for the receiver 85 is providedby the line 90 which is tapped to the liquid line 78 and which has theoat valve 91 interposed therein. Said oat valve maintains a desiredliquid level within the low temperature receiver 85 when the hightemperature accumulator 74 and the low temperature accumulator 86 are atthe same pressure.

The receiver 85 and the accumulator k86 are connected by the line 92having the pressure differential regulator 93. As previously described,the regulator 93 bleeds the gas from the receiver 85 to the accumulator86 in a controlled manner and thus maintains the desired lower prepssurein the accumulator. The refrigerant feed line 94 supplies liquid fromthe receiver 85 to the coil 95 and the same connects with the lowtemperature evaporators 96. The coil is submerged in the liquid withinthe accumulator for sub-cooling. The evaporators have the expansionvalves 97 and said evaporators deliver the evaporated gas and any liquidrefrigerant entrained therein through the line 98 to the low temperatureaccumulator 86. The suction line 61 completes the system since theevaporated gas from the accumulator 86 is returned by said line to thecompressor 63. For returning the liquid refrigerant to the respectivereceivers and in a manner to by-pass the compressors, the apparatusemploys the return system of Figure 1, including the trap and three-wayvalve, all as described. Accordingly, the lines 99 and 10i) for the highand low Vstages respectively are included in the said return system.

Figure 3 illustrates a balanced single stage circulating systemproviding two suction pressures. The suction line has connection withthe compressor 111 and the high pressure discharge line 112 from saidcompressor connects with the condenser 113. The outlet line 114 from thecondenser leads to the receiver 115V and -sra'id line has interposedtherein the pilot receiver 116 and the pilot operated float valve 1-17for maintaining the desired liquid level within the receiver. The gasfrom the receiver 115 is passed in a controlled manner to the hightemperature accumulator 11S by the line 119 having the pressuredifferential regulator 120. The liquid from the receiver is delivered byline 121 to the cooling coil 122 submerged within the liquid in theaccumulator. Said accumulator 11S in this modification of the inventionis provided with a float valve 124 which maintains a minimum level ofliquid refrigerant within the accumulator when the high temperatureevaporators are not in operation. The valve is of the normally closedtype. From the coil 122 the liquid refrigerant line 121 leads to thehigh temperature evaporators 125. Said evaporators are provided with theexpansion valves 126 and their suction line 127 returns the evaporatedgas and entrained liquid to the accumulator 118.

The liquid from the accumulator 11S is delivered by line 130 to the coil131 located within the low temperature accumulator 132. The coil 131 issubmerged within the liquid in the low temperature accumulator forsubcooling and said coil is in turn connected to the low ternperatureevaporator 133. The accumulator 118 acts as a receiver for the lowtemperature evaporator and according the line 130 must be provided withthe valve 134. The expansion valve 135 controls the feed of the liquidrefrigerant to the evaporator 133 and the evaporated gas together withany entrained liquid is returned by the suction line connection 136 tothe accumulator 132. The line 128 connects the accumulators 118 and 132and said line is provided with the differential pressure regulator 129.The intermediate pressure thus maintained in 11S is adequate to feed allthe low temperature evaporators.

The apparatus of Figure 3 incorporates liquid return systems basicallysimilar to that as described for Figure l. For example, liquidrefrigerant will drain by gravity from accumulator 118 by means of theline 137 to the trap 138. In a similar manner, liquid refrigerant fromaccumulator 132 will drain by gravity through the line 139 to the trap140. Both traps are equipped with differential float switches such as141 and 142 and by means of the three-way valves 143 and 144 it ispossible to alternately connect the traps to the high pressure dischargeline 112 for evacuating the traps and to the respective accumulators 118and 132 for venting the traps. Line 145 functions to connect the trapsto the high pressure discharge line 112 whereas line 146 and 147 willfunction to connect the traps to their respective accumulator. When thetraps are evacuated the liquid refrigerant is delivered by line 148 tothe receiver 115.

The apparatus of Figure 4 consists of a balanced circulating systemwherein a single stage is employed, the same having a single suctionpressure. The suction line 150 connects with the compressor 151. Thehigh pressure discharge line 152 leads to the condenser 153 and theliquid from the condenser is delivered by line 154 t0 a receiver 155.Said line 154 has interposed therein the pilot operated valve 157 whichmaintains the desired liquid seal in the pilot receiver 156. The gasfrom receiver 155 is delivered in a controlled manner to the suctionaccumulator 158 by the line 159 having the pressure differentialregulator 166. The liquid refrigerant from the receiver 155 is deliveredby line 161 to the coil 162. ln accordance with the invention, the coil162 is submerged within the liquid refrigerant contained within theaccumulator 15S. From the coil 162 the liquid refrigerant feed line 161leads to the evaporator 163. Said evaporator may consist of one or morecoils in parallel arrangement each having an expansion valve 164 andeach connecting by means of the suction line 165 to the accumulator 158.The system is completed by the suction line 150 which delivers theevaporated gas from the accumulator to the compressor.

The apparatus of Figure 4 employs the liquid return system as hereindescribed for returning the liquid refrigerant from the accumulator tothe receiver and in a manner to by-pass the compressor. Accordingly,line? 166 will drain liquid refrigerant from the accumulator by gravityand deliver the same to the trap 167. The trap in turn is provided withthe differential oat switch 168 and with a three-way valve 176.Actuation of the valve is controlled by the float switch for alternatelyconnecting the trap to the high pressure discharge line 152 and to theaccumulator 153 whereby the trap can be alternately evacuated andvented. Line 171 connects the three-way valve with line 152 whereas thevalve is connected by line 172 with accumulator 158. When the trap 167is evacuated, its charge of liquid refrigerant is delivered by line 173to the receiver 155.

The invention is not to be limited to or by details of construction ofthe particular embodiment thereof illustrated in the drawings, asvarious forms of the device will of course be apparent to those skilledin the art without departing from the spirit of the invention or thescope of the claims.

What is claimed is:

l. In a refrigerating system, in combination, an evaporator, a feed linefor supplying refrigerant under pressure to said evaporator in an amountgreater than the evaporator is capable of evaporating, a suction linefor drawing off the vaporized and liquid refrigerant from theevaporator, an accumulator in the suction line for trapping the liquidpassing through the evaporator, said feed line including a coil havinglocation within the accumulator and below the level of the liquidrefrigerant within the accumulator for cooling the refrigerant flowingin the feed line in advance of supplying the refrigerant to theevaporator, and liquid return means including a reservoir for receivingand temporarily storing the excess liquid trapped in said accumulator, aconduit connecting said reservoir with the feed line in advance of thecoil, means operable in response to changes in the level of the liquidin the reservoir, and valve means controlled by said level responsivemeans for introducing vaporized refrigerant from the pressure side ofthe system into said reservoir to force the liquid from the reservoirand into the said conduit for eventual delivery to the feed line.

2. A refrigerating system as defined by claim 1, additionally includinga second evaporator and a second accumulator, the second accumulatorbeing located in the suction line of the said second evaporator fortrapping any liquid passing through the second evaporator, a feed linefor the second evaporator and having connection with the first mentionedaccumulator for feeding liquid refrigerant trapped by the rst mentionedaccumulator to the second evaporator, said feed line for the secondevaporator including a coil located in the second accumulator beloW thelevel of the liquid refrigerant within the accumulator for cooling therefrigerant flowing in the feed line in advance of feeding the same tothe second evaporator, and liquid return means for returning the excessliquid refrigerant from the second accumulator to the first mentionedfeed line.

3. In a refrigerating system, in combination, an evaporator, arefrigerant feed line connecting with the evaporator and including acompressor, a condenser and a receiver, a suction line for returningevaporated gas from the evaporator to the compressor, an accumulator inthe suction line for trapping any liquid refrigerant returning with thegas, a coil in the feed line and located in the accumulator below thelevel of the liquid refrigerant in the accumulator for cooling therefrigerant flowing in the line in advance of supplying the same to theevaporator, conduit means connecting the receiver with the accumulator,said means including a differential pressure regulator for controllingflow of the refrigerant gas from the receiver to the accumulator in acontrolled manner, whereby the receiver is maintained at a pressurebelow condenser pressure but above evaporator pressure, a secondevaporator and a second accumulator, a suction line for the secondevaporator and having the second accumulator interposed in the line fortrapping any'liquid refrigerant passing-through the second evaporator, asecond refrigerant feed line connecting the rst mentioned accumulatorwith the second evaporator for feeding liquid refrigerant trapped by theiirst mentioned accumulator thereto, 4the second feed line having a coillocated in the second accumulator below the level of the liquidrefrigerant within the accumulator for cooling the refrigerant flowingin the line in advance of feeding the same to the second evaporator, andliquid return means associated with the accumulators respectively forreturning the excess liquid from the accumulators to the receiver.

4. In a refrigerating system, in combination, a compressor, a condenser,an evaporator and a receiver, said receiver supplying liquid refrigerantunder pressure to said evaporator in an amount greater than theevaporator is capable of evaporating, a suction line for drawing olf thevaporized and liquid refrigerant from the evaporatortan accumulator insaid suction line for trapping the liquid passing through theevaporator, a liquid feed line connecting the receiver with theevaporator, a coil in the feed line located within the accumulator andsubmerged 1n the liquid trapped by the accumulator for cooling theliquid refrigerant flowing in the line in advance of delivering it tothe evaporator, means connecting the receiver with the accumulator, saidmeans including a differential pressure regulator for maintaining apressure Vin the receiver below condenser pressure and above evaporatorpressure, and liquid refrigerant return means for draining the excessliquid from the accumulator and for returning the same to the receiverso as to by-pass the compressor of the system.

5. In a refrigerating system, in combination, a high temperatureevaporator, arefrigerant feed line connecting with said evaporator andincluding a compressor, a condenser and a receiver, a suction line forreturning evaporated gas from the evaporator to the compressor, anaccumulator in the suction line for trapping any liquid refrigerantreturning with the gas, a coil in the feed line and'located in theaccumulator below the level of the llquid refrlgerant in the accumulatorfor cooling the refrigerant flowing in the line in advance of supplyingthe same to the evaporator, means connecting the receiver with theaccumulator, said means including a differential pressure regulator formaintaining a pressure in the receiver below condenser pressure butabove evaporator pressure, a low temperature evaporator, a secondaccumulator in the suction line from the low temperature evaporator fortrapping liquid refrigerant returning in said line, a second feed lineconnecting the iirst mentioned accumulator with the low temperatureevaporator for supplying the liquid refrigerant from within theaccumulator to the said evaporator, and said second feed line includinga coil having location Within the second accumulator below the level ofthe liquid refrigerant therein for cooling the refrigerant flowing inthe second feed line in advance of supplying the refrigerant to the lowtemperature evaporator.

h 6. A refrigerating system as defined by claim 5, additionallyincluding liquid refrigerant return means for the iirst mentionedaccumulator and for the second accumulator respectively, each said meansdraining the excess liquid from its accumulator and returning the sameto the receiver.

7. in a refrigerating system, in combination, a high temperatureevaporator, an accumulator connected to the suction line of saidevaporator, a refrigerant feed line connecting with the evaporator andincluding a compressor,l a condenser and a receiver, a coil in the feedline and ilocated in the accumulator below the level of the liquidrefrigerant in the accumulator for cooling the refrigerant ilowing inthe feed line inV advance of supplying the same to the evaporator,conduit means connecting the receiver with the accumulator, said meansincluding a differential pressure regulator for controlling flow of therefrigerant gas from the receiver to the accumulator in a controlledmanner, whereby the receiver is maintained at a pressure below condenserpressure but above evaporator pressure, a low temperaturerevaporator, asecond accumulator connected to the suction line of the low temperatureevaporator, a second refrigerant feed line connecting the rst mentionedaccumulator with the low temperature evaporator for feeding liquidrefrigerant from the rst mentioned accumulator to the said evaporator, acoil in the second feed line and located in the second accumulator belowthe level of the liquid refrigerant therein for cooling the refrigerantilowing in the line in advance of feeding the same to the lowtemperature evaporator, second conduit means joining the first mentionedaccumulator with the second accumulator, said means including adifferential pressure regulator for controlling flow of the evaporatedrefrigerant from the iirst mentioned accumulator to the secondaccumulator, whereby the first mentioned accumulator is maintained at apressure below receiver pressure but above that of the low temperatureevaporator, and a suction line `connecting the second accumulator withthe compressor.

8. A refrigerating system as defined by claim 7, additionally includingliquid refrigerant return means for the iirst mentioned accumulator andfor the second accumulator respectively, each said means returning theexcess liquid refrigerant from the accumulators to the receiver.

9. In a refrigerating system, in combination, a high temperatureevaporator, a lirst accumulator connected to the suction line of saidevaporator, a refrigerant feed line connecting with the evaporator andincluding a compressor, a condenser and a first receiver, a coil in thefeed line and located in the accumulator below the level of the liquidrefrigerant in the accumulator for cooling the refrigerant ilowing inthe feed line in advance of supply- `ing the same to the evaporator,conduit means connecting the rst receiver with the first accumulator,said means including a dilferential pressure regulator for controllingflow of the refrigerant gas from the receiver to the accumulator in acontrolled manner, whereby the receiver is maintained at a pressurebelow condenser pressure but above the pressure of the high temperatureevaporator, a low temperature evaporator, a second receiver, a secondaccumulator connected to the suction line of said low temperatureevaporator, a second refrigerant feed line connecting the rstaccumulator with the low temperature evaporator for feeding liquidrefrigerant from the accumulator to said evaporator, said second feedlineincluding the said second receiver and a second coil, Vsaid coilhaving a location within the second accumulator below the level of theliquid refrigerant therein for cooling the refrigerant flowing in thefeed line in advance of supplying the same to the low temperatureevaporators, conduit means connecting the second receiver with thesecond accumulator, said means including a dierential pressure regulatorfor controlling ow of the refrigerant gas from the receiver to theaccumulator, whereby the second receiver is maintained at a pressurebelow condenser pressure but above the pressure of the low temperatureevaporator, and liquid return means for returning the excess liquidrefrigerant from the accumulators to the receivers respectively.

References Cited in the file of this patent UNITED STATES PATENTS2,841,962 Richard ,.--.Y July 8, 1958

